Method for the production of semiconductor elements made of an intermetallic compound



1964 MASARU YAMANO ETAL 3,162,531

METHOD FOR THE PRODUCTION OF SEMICONDUCTOR ELEMENTS MADE OF AN INTERMETALLIC COMPOUND Filed March so, 1961 FIG. I.

INVENTOR.

United States Patent 3,162,531 lVIETHOD FOR THE PRODUCTION OF SEMICON- DUCTOR ELEMENTS MADE OF AN INTER- METALLIC COMPOUND Masaru Yamano, Hirakata, Osaka, and Eiichi Komatsu, Goganzuka, Itami, Japan, assignors to Sanyo Electric Co., Ltd., Moriguchi, Osaka, Japan Filed Mar. 30, 1961, Ser. No. 99,466 4 Claims. (Cl. 75-226) This invention relates to a novel and improved process for producing semiconductive elements made of an intermetallic compound, and more particularly to a method for the production of thermoelements of a definite shape by means of hot-pressing.

The primary object of the invention is the presentation of a new and useful method for producing definitely shaped, semiconductor elements of an intermetallic compound by hot-pressing through the utilization of heat of chemical combination.

Another object of the invention is to provide a simple process for the manufacture of thermoelements which is substantially foolproof in operation and which greatly enhances thermoelectric properties of the products.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention is schematically illustrated by way of example in the accompanying drawings, wherein:

FIG. 1 is a sectional view of a die pressing device, schematically illustrating the principle of the process according to the invention; and

FIG. 2 shows schematically and partly in section apparatus adapted for carrying out the process of the invention.

The process according to the invention is carried out in principle using a die pressing device as shown schematically in FIG. 1. The die pressing device comprises a die 11 and a pair of punches 12 and 13. The material 14 is inserted in the die 11 and pressed by the upper and lower punches 12 and 13 to be formed into a definite shape according to the shapes of the die and punches. Preferably both of punches 12 and 13 are simultaneously movable toward each other in pressing operationthis is of the so-called double punch type, however, only one punch may be movable while the other is stationary this is of the so-called single punch type.

In the practice of the present invention, the material 14 is prepared by evenly mixing two or more component elements in the form of powder, inserted in the die 11 to deposit on the end surface 16 of the lower punch 13, and then compressed between the end surface 15 of the upper punch 12 and the end surface 16 of the lower punch 13, either by pushing down the upper punch 12 toward the stationary lower punch 13 or by pushing down the upper punch 12 and simultaneously pushing up the lower punch 13. The compressed material 14 is then heated, with the pressure applied, by a suitable means until its certain portion attains to an ignition temperature at which the component elements begin to combine into an intermetallic compound. This chemical combination is an exothermic reaction and the neighbourhood of the initially ignited portion is in turn heated to the ignition temperature by heat of combination. The progress of the chemical combination in the material may, therefore, be made as a chain reaction and completed over the whole material in a moment with the result of expansion of the combined material, which causes to press back the punches 12 and 13. The material thus combined has the structure of crystals of a semiconductor. According to the invention, while the heat produced is being lost through conduction outwardly, the material 14 is hot-pressed to be formed into a definite shape by the 3,162,531 Patented Dec. 22, 1964 punches 12 and 13. The product may be taken out by pushing up the lower punch 13.

In summing up, the invention is a method for obtain ing a definitely shaped produced by hot-pressing the material through the utilization of heat produced by chemical combination in the material. Thermoelements produced according to the invention may have thermo-electric properties as desired.

There is shown in FIG. 2 in a diagrammatic and schematic manner a typical, illustrated and preferred form of apparatus according to the invention, by which the process of the present invention is preferably carried out. In the following detailed description, the apparatus will be described in some detail together with certain features of its operation, and the process of the invention will then be described with reference to such apparatus although the process may, obviously, be carried out by many other and widely different forms of apparatus.

FIG. 2 shows schematically a die pressing machine according to the invention, comprising a forming die 21 and a pair of punches 22 and 23. The forming die 21, which is shaped in the form of a tube, may be made of metal which can be electrically heated so that the material within the die 21 may be heated when the die is supplied with an electric current. However, it will be noted that the present invention may also be carried out with use of any other heating mechanism, for example a warming mechanism of high frequency-type. The die 21 is required to have a good strength at a high temperature. In order to satisfy the above two requirements, the die 21 may be made of heat-resisting steel such as 18%-chrome steel, l3%-chrome steel or l8-8-steel (18% chrome-8% nickel-steel). The forming die 21 is supported by such a non-metallic insulator 24 as Teflon (polytetrafluoroethylene). The support 24 may have the nature of a reinforceme'nt for the die 21. 25 and 26 are annularly shaped, conductive plates which are respectively connected to the opposite ends of the die 21 for supplying it with an electric current. The upper and lower punches 22 and 23 are vertically arranged in alignment and movable in the vertical direction. In the non-operating condition, the upper punch 22 is apart 'from the die 21 while the lower punch 23 is stationary in a certain position within the die 21. The powdered material 27 for a semiconductor is inserted into the die 21 to be deposited on the top surface of the lower punch 23 and then compressed by introducing the upper punch 22 into the die 21, the lower punch 23 being stationary at the original position or simultaneously pushed upward a little. The upper punch 22 is connected through an oil dumper mechanism generally indicated at 28 to a pushing rod 29 to which an actual pushing force is applied in the vertically downward direction. 30 is a packing for sealing the oil in the oil dumper mechanism 28. 31 is a pressure gauge for indicating the oil pressure in the oil dumper 28 and 32 is a switch which is operable in relation to rise of the oil pressure so as to cut oil the supply of an electric current to the die 21 when the oil pressure rises to a predetermined pressure.

The compressed material 27 is in turn heated by electrically heating the die 21. The peripheral portion of the material 27 attains first to an ignition temperature at which chemical combination of the component elements can be started. The chemical combination extends over the whole material in a moment as a chain reaction because the chemical combination is an exothermic reaction producing heat. The heated material whose component elements have been combined into an intermetallic compound is simultaneously expanded whereby the upper punch 22 is pushed back upwardly in opposition to the oil pressure in the oil dumper 28, while the rod 29 and the lower punch 23 are maintained stationary. The termination of chemical combination may be found in relation to rise of the oil pressure in the Bil dumper 38. The oil pressure in the oil dumper 38 may be indicated by the pressure gauge 31 and the time of completion of chemical combination in the material 27 may be detected by the pressure-operable switch 32. The pressure-operable switch 32 switches ofl? the circuit for supplying the die 21 with an electric current when the oil pressure reaches a certain, high pressure which is probably near to the maximum pressure and at which chemical combination in the material has been over, in such a manner that the circuit will never be switched on after then even if the oil pressure falls down. When heat of the material is being lost through conduction outwardly, the combined material is automatically hot-pressed by the oil pressure to be formed into a definite shape. However, another positive pressing force may be applied to the punches by any other means.

With reference to the following examples, which describe some preferable methods for the production of thermoelements according to the present invention, it is supposed that the die 21 used therein is madeof 18%- chrome steel having specific resistivities of 6m cm. at 25 C. and 1145 cm. at 650 C., respectively, and shaped in the form of a tube having an internal diameter of 10 mm., an outer diameter of 16 mm. and a length of 100 mm. It is also noted that each product has a diameter of 10 mm. and a length of 20 mm., a Weight of about 12 gram.

Example 1 Percent in weight Bismuth powder (150 mesh pass) 52.3 Tellurium powder (150 mesh pass) 47.7

The above quantities of bismuth and tellurium are mixed up. The material thus prepared is inserted into the die and compressed between the upper and lower punches with the pressure as given Within the range from 1.5 to 2.5 tons/cm. preferably Within the range from 1.8 to 2.0 tons/cmF. The compressed material is then heated by electrically heating the die. It takes 194 seconds after an electric current of 1.0 volt A.C. and 230 amperes has been applied to the die, until the peripheral portion of the compressed material attains to the ignition temperature of 240 C. at which the elements in the material commence to combine into an int-ermetallic compound. The chemical combination in the material progresses as a chain reaction and concludes taking about one second. The maximum temperature of the material during the reaction reaches 550 C. and the maximum pressure which is produced in the oil dumper would reach 5.3 tons/crnf The die may be cut oil from the supply of an electric current when the oil pressure in the oil dumper reaches 5.0 tons/cmP, as chemical combination in the material has been already completed then. During the time in which heat of the material is being lost through conduction outwardly, the material is hotpressed under the oil pressure and formed into a definite shape. When the oil pressure gauge indicates 4 tons/ cm. or below, the definitely shaped product may be taken out by removing the upper punch from the die and pushing up the lower punch. The thermoelement thus produced is of p-type and has the following thermoelec tric properties at the room temperature of 25 C.:

Thermal electromotive force: ::195 ,uv./deg. C. Electric conductivity: 0:800 mho Thermal conductivity: K:2.0X watt/ cm. deg. C.

Selenium powder (150 mesh pass) 7.2 The above quantities of bismuth, tellurium and selenium are mixed up. The material thus prepared is compressed, heated, and hot-pressed in the same manner as Example 1. The ignition temperature is 210 C. and it takes 169 seconds until the peripheral portion of the material is heated to the ignition temperature. The die may be cut off from the supply of the electric current when the pressure gauge indicates 5.5 tons/cmEa The maximum temperature during the reaction would rise to 580 C. and the maximum pressure would reach 5.8 tons/ cm. The reaction of chemical combination concludes for 0.5 second. The thermoelement thus produced is of n-type and has the following thermoelectric properties at the room temperature of 25 C.:

11:190 uv/deg. C.

(7:100 mho I =1.3 X 10- watt/ cm. deg. C.

Example 3 Percent in weight Bismuth powder mesh pass) 20.9 Antimony powder (150 mesh pass) 23.3 Tellurium powder (150 mesh pass) 50.8

The above quantities of bismuth, tellurium and selenium are mixed up. The material thus prepared is compressed, heated, and hot-pressed in the same manner as Example l. The ignition temperature is 270 C. and it takes 224 seconds until the ignition temperature is obtained. The die may be cut off from the supply of the electric current when the pressure gauge indicates 4.5 tons/cmF. The maximum temperature during the reaction would rise to 460 C. and the maximum pressure would reach 4.7 -tons/cm. The reaction of chemical combination concludes taking about 2.5 seconds. The thermoelement thus produced is of p-type and has the following thermoelectric properties at the room temperature of 25 C.:

oc= ,uV./dg. C. 1:900 mho K:1.2X10 2 watt/cm. deg. C.

What we claim is:

1. A method for the production of semiconductor thermoelements made of intermetallic compounds which comprises preparing a mixture in powder form of the component elements bismuth and a member selected from the group consisting of tellurium, selenium, antimony, and mixtures of the foregoing, compressing saidrmixture in a die, heating said mixture while under pressure in said die to an ignition temperature at which an exothermic reaction occurs between the component elements to form an intermetallic compound, permitting the exothermic reaction to proceed rapidly to completion with evolution of heat and expansion of the contents of the die, and simultaneously forming the hot intermetallic compound formed by the exothermic reaction into a define shape by hot-pressing through the utilization of the heat and expansion force given oh by the exothermic reaction.

2. A method for the production of semiconductor thermoelements made of an intermetallic compound which comprises preparing a mixture in powder form which comprises, by Weight, about 52.3% bismuth and about 47.7% tellurium, the size of the particles of said mixture being less than 150 mesh, compressing said mixture in a die at a pressure of between about 1.5 and 2.5 tons/cm. progressively heating said mixture to about 240 C. to initiate an exothermic reaction between hismuth and tellurium to form an intermetallic compound, permitting the exothermic reaction to proceed rapidly to completion With evolution of heat and expansion of the contents of the die, and simultaneously forming the hot intermetallic compound formed by the exothermic reaction into a definite shape by hot-pressing the contents of the die through the utilization of the heat and expansion force given off by the exothermic reaction under a pressure up to about 5.3 tons/cm 3. A method for the production of semiconductor thermoelements made of an intermetallic compound which comprises preparing a mixture of component ele- I ments in powder form which comprises, by weight, about 54.5% bismuth, 38.3% tellurium and 7.2% selenium, the size of the particles of said mixture being less than 150 mesh, compressing said mixture in a die at a pressure of between about 1.5 and 2.5 tons/cm. heating said mixture while under said pressure to a temperature of about 210 C. to initiate an exothermic reaction between the component elements to form an intermetallic compound,

tween the component elements to form an intermetallic compound, permitting the exothermic reaction to proceed rapidly to completion with evolution of heat and expansion of the contents of the die, and simultaneously forming the hot intermetallic compound formed by the exothermic reaction into a definite shape by hot-pressing at a pressure up to 4.7 tons/cm. through the utilization of the heat and expansion force given off by the exothermic reaction.

permitting the exothermic reaction to proceed rapidly to 10 completion with evolution of heat and expansion of the References Cited in the file of this Patent contents of the die, and simultaneously forming the hot intermetallic compound formed by the exothermic reac- UNITED STATES PATENTS tion into a definite shape by hot-pressing the contents of 1,896,854 Taylor Feb. 7, 1933 the die at a pressure up to 5.8 tons/cm. through the 5 2,022,528 Taylor Nov, 26, 1935 utilization of the heat and expansion force given off by 2,149,596 Gillett et a1, Mar. 7, 1939 the exothermic reaction. 2,175,899 Kelly Oct. 10, 1939 4. A method for the production of semiconductor 2,437,127 Richardson Mar. 2, 1948 thermoelements made of an intermetallic compound 2,835,573 Hausner May 20, 1958 which comprises preparing a mixture of component ele- 2,852,980 Douglas Sept. 20, 1958 ments in p r form comprising, y Weight. about 2,922,710 Dombrowski et al. Jan. 26, 1960 20.9% bismuth, about 23.3% antimony, and about 50.8% 2,982,014 Hartwig May 2, 1961 tellurium, said mixture having a particle size of less than 2,993,786 Robofi et a1 July 25, 1961 about 150 mesh, compressing said mixture in a die at a 3,082,277 Lane et a1, Mar. 19, 1963 pressure of between about 1.5 and 2.5 tons/cm. heating said mixture while under pressure to a temperature FOREIGN PATENTS of about 270 C. to initiate an exothermic reaction be- 1,064,537 Germany P 3, 1959 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,162,531

December 22, 1964 Masaru Yamano et al.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 24, for "6 ,152" read 10 column 4,

line 14, for Inho" read 1000 mho "define" read definite line 53, for

Signed. and sealed this 6th day of Julyl965.

(SEAL) Attest:

EDWARD J. BRENNER Commissioner of Patents ERNEST W. SWIDER Attesting Officer UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No a 3 ,162 ,531 December 22 1964 Masaru Yamano et al,

It is hereby certified that error appears in the above numbered paten't requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 24, for "6 10" read 60 10 column 4, line 14, for "100 mho" read 1000 mho line 53, for "define" read definite Signed and sealed this 6th day of July 1965,

(SEAL) A nest:

ERNEST W. SWIDER EDWARD J. BRENNER Commissioner of Patents Attesting Officer UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,l62 ,531 December 22 1964 Masaru Yamano et ale It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 24, for "6 9" read 60119 column 4, line 14, for "100 mho" read 1000 mho line 53, for "define" r-pad definite Signed and sealed this 6th day of July 1965 (SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. A METHOD FOR THE PRODUCTION OF SEMICONDUCTOR THERMOELEMENTS MADE OF INTERMETALLIC COMPOUNDS WHICH COMPRISES PREPARING A MIXTURE IN POWDER FORM OF THE COMPONENT ELEMENTS BISMUTH AND A MEMBER SELECTED FROM THE GROUP CONSISTING OF TELLURIUM, SELENIUM, ANTIMONY, AND MIXTURES OF THE FOREGOING, COMPRESSING SAID MIXTURE IN A DIE, HEATING SAID MIXTURE WHILE UNDER PRESSURE IN SAID DIE TO AN IGNITION TEMPERATURE AT WHICH AN EXOTHERMIC REACTION OCCURS BETWEEN THE COMPONENT ELEMENTS TO FORM AN INTERMETALLIC COMPOUND, PERMITTING THE EXOTHERMIC REACTION TO PROCEED RAPIDLY TO COMPLETION WITH EVOLUTION OF HEAT AND EXPANSION OF THE CONTENTS OF THE DIE, AND SIMULTANEOUSLY FORMING THE HOT INTERMETALLIC COMPOUND FORMED BY THE EXOTHERMIC REACTION INTO A DEFINITE SHAPE BY 